With some devices of prior art, an endless belt such as referred to above will extend so as to contact a plurality of spaced apart driving pulleys with contact being effected by a plurality of tightening rolls which, on the one hand, serve in guiding the belt and which, on the other hand, act to force the belt against the driving pulleys of spinning rotors and/or fiber separating cylinders.
Because of the relatively high rotation rates of modern open-end spinning machines, the tightening rolls and, consequently, the driving belt, are exposed to considerable vibration, in spite of the fact that the rolls are usually spring-loaded. In this regard, the mounting of tightening rolls on swing legs (as provided for, e.g., in Czechoslovak Inventor's Certificate No. 198 068) has proved inadequate or insufficient, because of the effects produced by belt vibration. These effects include wear or fatigue of the swing leg pivots, inaccurate belt guide positioning, fluctuations in the belt thrust power and, consequently, oscillations of the drive as a whole. Negative consequences of these effects include an increased noise level and a shorter lifetime of the mounting.
Attempts have been made to eliminate these drawbacks and to this end the tightening rolls have been mounted on elastic or resilient legs in the form of single leaf spring (British Patent Specification No. 1,349,263 and corresponding West-German Application 2,048,959). Due to the relatively low flexural rigidity of such legs, their torsional rigidity is also low so that the tightening rolls are prone to tilting to the sides. Consequently, the belt can be incorrectly guided, slide off the rolls, come into engagement with the flanged edges of the rolls and become worn by these edges. As a result the lifetime and drive reliability of the belt are markedly reduced, even apart from the above-mentioned rise in noise level produced with such devices.